I have done some tests with this exporter since I do the majority of my development work in Unity these days.
The results are dismal at best, at worst totally broken. I have a list as long as your arm outlining the problems you can expect to see, but as a sample look towards HIfi’s own description of the results.GitHub

Unity to High Fidelity Exporter. Contribute to highfidelity/unity-to-hifi-exporter development by creating an account on GitHub.

I tried this a year ago and have no idea what the results might be with Hifi’s current release.

Since there has been no movement on this project for nearly a year I would expect unresolvable problems using the newest Unity releases, if you must do this thing then stick with the old Unity version.

Look at the list of known limitations, that will tell you whats not going to happen.
ie. Particles and scripts are ignored.
Parents which skew their children will not import correctly.
FBX format will only recognize diffuse maps and normal maps when exporting, the non support of specularity and hardness maps is a problem in terms of good rendering finish.

Some of the issues I encountered:
Textures are completely wrong, Unity primitives which are textured in Unity are all messed up including colors, mixed up textures and incorrect mapping, but mesh objects built and textured externally and imported into Unity are in better shape but still have problems, shader order seems to be reversed so the spec maps become the albedo etc. UV mapping remains intact. Although some objects arrived completely blank. Invisible game objects arrived as white primitives.

In short with the current state of this importer I am tempted to suggest it would be more work to import an existing complex project and then try to fix it, and it will still not look or behave anything like the original and it will probably be better to rebuild the project entirely in High Fidelity.

Got it. There was 1 new user recently who actually had success with it. I wasn’t expecting particle or script support, mainly just an easier way to look at what I’m building without being confined to building in HiFi alone.

I questioned this one, I think it was aimed at grabbing some of the vrchat users… Just don’t get the use case here… This is like admitting your own build tools stink, using another competitor tool seems like an odd workaround. (as opposed to improving build tools in Hifi)

Same thing goes for the unity avatar exporter… why is HiFi even spending a dime on these types of tools/converters.

I do agree,
They better focus on having an easy avatar provider, that might attract a bit more people.
This makes flee everyone that would like to invest more time here and have it’s own avatar.
It’s what we have right in Hifi, a comfortable avatar system… pushing on this would be a good thing.

Well if the shoe fits . Its the very reason I spend so little time in Hifi and so much time in Unity. Unity is a dream to work in.

But to me the use case is where I have dozens of projects already built in Unity and it would have been wonderful to just be able to port them over easilly, I thought this was a brilliant proposal. But the reality is it just doesnt work right. There is so much work to fix them after import that its just not worth it.